In the field of non-volatile memories, flash memory scaling to lower dimensions has become a real issue. Technologies to face this challenge are ferroelectric, magnetic and phase change memories, the latter one being promising for the replacement of flash and showing characteristics that may allow replacement of other types of memories such as DRAM. Phase change memories are a possible solution for the unified memory being an important step in the electronics art. OTP (“on time programmable”) and MTP (“multiple times programmable”) memories open a field that may present a great opportunity for phase change memories as well.
Phase change memories are based on a reversible memory switching using, for instance, chalcogenide materials. The ability of these materials to undergo fast phase transition has led to the development of rewritable optical media (CD, DVD). The chalcogenide phase change materials may be divided in two classes which are slightly different compositions, based on their crystallization mechanism. The “nucleation dominated” material GeTe-Sb2Te3 tie line such as Ge2Sb2Te5 are generally used in ovonic unified memory (OUM) devices. In this concept, the phase change material may be in contact with a bottom-resistive electrode to switch reversibly to a small volume of phase change material. “Fast growth material”, known in optical storage application (CD-RW/DVD+RW), enable very fast switching (for instance 10 ns) with a proper phase stability.
Thus, phase change materials may be used to store information. The operational principle of these materials is a change of phase. In a crystalline phase, the material structure, and thus, properties, are different from the properties in the amorphous phase.
US 2003/0075778 A1 discloses a programmable resistance memory element. The active volume of memory material is made small by the presence of a small area of contact between the conductive material and the memory material. Forming a region of conductive material and an intersecting sidewall layer of the memory material creates the area of contact. The region of conductive material is preferably a sidewall layer of conductive material.
The endurance of a phase change memory cell may be denoted as the number of cycles a cell can be switched between a low resistance value (SET state) and a high resistance value (RESET state). However, the endurance of conventional phase change memory cells may be too small.